Transistor gate forming methods and transistor structures

ABSTRACT

A transistor gate forming method includes forming a metal layer within a line opening and forming a fill layer within the opening over the metal layer. The fill layer is substantially selectively etchable with respect to the metal layer. A transistor structure includes a line opening, a dielectric layer within the opening, a metal layer over the dielectric layer within the opening, and a fill layer over the metal layer within the opening. The metal layer/fill layer combination exhibits less intrinsic less than would otherwise exist if the fill layer were replaced by an increased thickness of the metal layer. The inventions apply at least to 3-D transistor structures.

TECHNICAL FIELD

The invention pertains to transistor gate forming methods and transistorstructures.

BACKGROUND OF THE INVENTION

A continuing interest exists in aggressively reducing feature sizes ofintegrated circuitry. In conventional semiconductor-based integratedcircuitry, polysilicon is often used as a gate electrode material in afield effect transistor (FET). However, polysilicon exhibits aresistivity generally considered too high for aggressive device scaling.Metal gate electrode materials have been identified to replacepolysilicon. While metal gate electrode materials appear to functioneffectively in simple configurations, difficulties can arise insubstituting metal gate electrode materials for polysilicon inthree-dimensional (3-D) transistor devices and other devices with a morecomplex configuration. Accordingly, a desire exists to developtransistor gate forming methods and transistor structures capable ofimplementing metal gate electrode materials.

SUMMARY OF THE INVENTION

In one aspect of the invention, a transistor gate forming methodincludes forming a gate metal layer within a gate line opening extendinginto a semiconductive substrate and forming a gate fill layer within theopening over the metal layer. The fill layer is substantiallyselectively etchable with respect to the metal layer. By way of example,the metal layer may be substantially selectively etchable with respectto the fill layer. Aspects of the invention apply at least to recessedaccess devices, word lines in trenches, and other three-dimensionaltransistor structures.

In another aspect of the invention, a transistor gate forming methodincludes forming a gate line opening extending into a semiconductivesubstrate, the opening having a semiconductive bottom and semiconductiveside walls. A gate dielectric is formed within the opening over thesemiconductive side walls and semiconductive bottom, the dielectriclayer having an insulative bottom and insulative side walls. A gatemetal layer is formed within the opening over the insulative bottom andinsulative side walls, the metal layer having a conductive bottom andconductive side walls. A gate fill layer is formed within the openingover the conductive bottom and conductive side walls. The methodincludes removing excess fill layer substantially selectively withrespect to the metal layer while exposing a portion of the metal layerunder the fill layer without exposing the gate dielectric under themetal layer.

In a further aspect of the invention, a transistor structure includes agate line opening extending into a semiconductive substrate, the openinghaving a semiconductive bottom and semiconductive side walls. A gatedielectric layer is within the opening over the semiconductive sidewalls and semiconductive bottom, the dielectric layer having aninsulative bottom and insulative side walls. A gate metal layer iswithin the opening over the insulative bottom and insulative side walls,the metal layer having a conductive bottom and conductive side walls. Agate fill layer is within the opening over the conductive bottom andconductive side walls. The metal layer/fill layer combination exhibitsless intrinsic less than would otherwise exist if the fill layer werereplaced by an increased thickness of the metal layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings. Reference numerals arenot used to identify some of the duplicated features having identical,repetitive structure where identification of the duplicates is clearlydiscernable.

FIGS. 1A-B to 5A-B are partial sectional views and FIGS. 1C to 5C aretop views at sequential process stages leading to formation of thetransistor structure in FIGS. 5A-C formed on a substrate according toone aspect of the invention.

FIGS. 6A-B to 8A-B are partial sectional views at sequential processstages leading to formation of the transistor structure in FIGS. 8A-Bformed on a substrate.

FIG. 9 is a partial sectional view of an alternative transistorstructure formed on a substrate according to another aspect of theinvention.

FIG. 10 is a diagrammatic view of a computer illustrating an exemplaryapplication of the present invention.

FIG. 11 is a block diagram showing particular features of themotherboard of the FIG. 10 computer.

FIG. 12 is a high level lock diagram of an electronic system accordingto an exemplary aspect of the present invention.

FIG. 13 is a simplified block diagram of an exemplary memory deviceaccording to an aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-B show partial sectional views and FIG. 1C shows a top view ofan in-process substrate prepared for formation of a conventionalrecessed access device (RAD), one of a variety of devices implementing3-D transistor configurations. “Recessed access” refers to a device witha word line (i.e., transistor gate) recessed into the semiconductivesubstrate (e.g., monocrystalline silicon wafer). Transistor gates thatsurround or partially surround transistor channels, as well as channelsthat surround or partially surround gates, are typical of 3-D devices ascompared to planar devices where the gate-to-dielectric-to-channelinterfaces are planar. As will be appreciated, substrate 10 in FIGS.1A-C possesses a structure processed to provide a gate that laterallysurrounds part of a transistor channel. In addition, the structure alsoprovides a transistor channel that laterally surrounds part of the gate.

The goal of RADs is to address some of the concerns from whichconventional MOSFETs may suffer. For example: 1) quantum-mechanicaltunneling (QMT) of carriers through thin gate oxide, 2) QMT of carriersfrom source to drain and from drain to body of a MOSFET, 3) control ofdensity and location of dopants in channel, source, and drain, and 4)unacceptable I_(off) currents.

Substrate 10 may be a semiconductive substrate. In the context of thisdocument, the term “semiconductor substrate” or “semiconductivesubstrate” is defined to mean any construction comprising semiconductivematerial, including, but not limited to, bulk semiconductive materialssuch as a semiconductive wafer (either alone or in assemblies comprisingother materials thereon), and semiconductive material layers (eitheralone or in assemblies comprising other materials). The term “substrate”refers to any supporting structure, including, but not limited to, thesemiconductive substrates described above.

A mask layer 12 shown in FIGS. 1A-C remains from the conventionalprocess used to form gate line openings 36 extending into substrate 10that will receive gate electrode material. Mask layer 12 may includesilicon nitride. Substrate 10 also includes a conventional n-typeconductivity doped tub 14 and a p-type conductivity doped well 16.Shallow trench isolation 18 and shallow trench isolation oxide 20 areformed within substrate 10 to separate individual transistors and otherdevices in an array of transistors that may be formed from thesubsequent transistor structure. A gate dielectric layer 22 formed onthe semiconductive bottom and semiconductive sidewalls of line openings36 may be a conventional gate oxide or other suitable material. Notably,portions of the bottom of line openings 36 are isolation 18 or 20, butother portions are semiconductive, as shown in FIG. 1B, to form atransistor channel discussed below.

Source/drain pillars 24 are formed between opposing source/drain walls26. An elevationally upper portion of individual pillars 24 andindividual walls 26 can ultimately become source/drain regions. Anelevationally lower portion of respective pillars 24 and respectivewalls 26 can ultimately become part of a channel region along with aportion of substrate 10 below line openings 36. Thus, a channel regioncan extend vertically from a source down through a pillar (or wall),through substrate 10 below a line opening, and vertically up through acorresponding wall (or pillar) to a drain. Pillars 24 may be drainsconnecting to a memory cell's capacitor and walls 26 may be a commonsource connecting to column address lines. For the exemplary RAD ofFIGS. 1A-C, lateral spacing between pillars 24 and walls 26 may be fromabout 300 to about 400 Angstroms. Spacing between pillars 24 in a givenrow sharing a common line opening 36 may be from about 500 to about 1500Angstroms.

In one approach shown in FIGS. 6A-B, a gate electrode layer 32 is formedwithin line openings 36 to a thickness generally sufficient to fill thegate line openings 36. A thickness that is at least about one-half ofthe spacing between pillars 24 normally would be sufficient or, for theFIGS. 6A-B example, from about 250 to about 750 Angstroms. However,FIGS. 6A-B also show cracks 34 from intrinsic stress that may resultwhen electrode layer 32 is deposited especially thick. Cracks generallyresult from high tensile stress, while lifting or other defects resultfrom high compressive stress. When forming titanium nitride as electrodelayer 32, cracks may occur apparently as the result of such high tensilestress. Cracking and/or lifting may occur for similar reasons in avariety of other conventional metal layers used for gate electrodes. Inthe context of the present document, “metal” layer refers to aconductive layer containing a metal compound or compounds (whichcompound may further include semimetals and/or non-metals), an elementalmetal, or a metal alloy. Elements considered to be metals in thisdocument do not include semimetals. Accordingly, semimetals B, Si, As,Se, Te, and At are not considered to be metals.

Exemplary materials for metal gates include titanium nitride, cobaltsilicide, nickel silicide, tantalum, tantalum nitride, tungsten nitride,and other thermally stable metal layers. A space is apparent in FIG. 6Abetween portions of electrode layer 32 that failed to “pinch off” duringdepositions, for example, because of high tensile stress in electrodelayer 32. Cracking in titanium nitride tends to appear wheneverthickness exceeds about 500 Angstroms. Also, seams inside line openings36 may fail to merge consistently, producing the visible mergeboundaries shown in FIG. 6A.

FIGS. 7A-B show the structure in FIGS. 6A-B after chemical-mechanicalpolishing, removing excess portions of electrode layer 32 elevationallyabove mask layer 12. The polishing step may be configured to stop onmaterial forming mask layer 12, such as silicon nitride or siliconoxide. Electrode layer 32 in FIGS. 7A-B is then etched to recess suchmaterial into line openings 36 as shown in FIGS. 8A-B. Reactive ionetching (RIE) in a LAM 9400 available from Lam Research Corp. inFremont, Calif. using 30-55 standard centimeter³/minute (sccm) Cl₂ and10-20 sccm CF₄ represents one example. As is apparent from FIG. 8A, suchetching may extend merge boundaries as cracks and widen insufficientlypinched-off seams further into electrode layer 32. Although not viewablein FIGS. 8A-B, stringers may form along walls 26, around pillars 24,and/or other parts of line openings 36 where electrode layer 32 isintended to be removed. Such stringers may result from thenon-uniformities discussed above and are difficult to remove. Also,although not viewable in FIGS. 8A-B, etching processes such as RIE andothers may damage exposed portions of gate dielectric 22 as electrodelayer 32 recedes from covering gate dielectric 22 and shrinks into lineopenings 36. Accordingly, it may be appreciated that the somewhat smallnon-uniformities of electrode layer 32 shown in FIGS. 6A-B may producesignificant defects after continued processing.

Those of ordinary skill often conduct series resistance (R_(s)) tests asa measure of proper device formation. A high variation in seriesresistance potentially indicates defects in some device structures. Alow series resistance is desired for a gate electrode since it functionsas a conductor. However, the defects shown in FIGS. 8A-B may produceunacceptably high R_(s), which seems to be a particular problem inprocesses forming gate electrodes in 3-D transistors.

According to one aspect of the invention, problems with formation ofelectrode layer 32 described herein may be reduced in a transistor gateforming method that includes forming a gate metal layer within a gateline opening extending into a semiconductive substrate and forming agate fill layer within the opening over the metal layer. The fill layeris substantially selectively etchable with respect to the metal layer.By way of example, the metal layer may be substantially selectivelyetchable with respect to the fill layer. Once those of ordinary skillappreciate the processes and advantages described herein, it will beunderstood that aspects of the invention apply to a RAD, as well as toother transistor structures. For example, the gate line opening may be aword line trench with the gate metal layer being formed within thetrench but not providing recessed access.

FIGS. 2A-C show the structure of FIGS. 1A-C after formation of a metallayer 28 within line openings 36 and formation of a fill layer 30 withinline openings 36 over metal layer 28. The metal layer may includetitanium nitride, among other materials mentioned herein and potentiallyothers known to those of ordinary skill, and may be formed by anyconventional method. Various types of chemical vapor deposition (CVD),such as atomic layer deposition (ALD), are particularly applicable.Physical vapor deposition (PVD) or supercritical fluid deposition (SFD)may be used instead. The fill layer may be semiconductive or conductiveif needed to provide conductivity for operation of completed transistorsor for some other reason identified by those of ordinary skill. However,the fill layer may be insulative, assuming that the metal layerfunctions adequately as a gate electrode.

Titanium nitride having a thickness of from about 100 to about 200Angstroms, preferably 150 Angstroms, has been identified as a metallayer thickness resulting in a suitable gate electrode. Bulk thicknessof a gate electrode formed with metal layer 28 is determined by itselevational height. Since metal layer 28 shown in FIGS. 5A-B may extendfrom about 600 to about 1,200 Angstroms, or preferably 1,000 Angstroms,up the side walls of gate dielectric 22, the elevational height mayprovide adequate bulk thickness even with a thin layer. Even thoughmetal layer 28 and fill layer 30 are shown as single layers in theFigures, it will be appreciated that multiple layers might be suitable.Even so, single layers are preferred for processing simplicity.

The fill layer may have a thickness of from about 1,500 to about 3,500Angstroms and may include polysilicon, tungsten, tungsten silicide, andother materials deposited by any conventional method, for example, CVD.If polysilicon, then it may be conductively doped. Silicon oxidedeposited from tetraethylorthosilicate (TEOS) as well asborophosphosilicate glass (BPSG) constitutes suitable insulativematerials that may be used for the fill layer. Desirable properties forthe fill layer include exhibiting a porosity greater than a porosity ofthe metal layer. A more porous or “spongy” material as the fill layertends to be deposited at significant thicknesses, such as greater than500 Angstroms, without exhibiting intrinsic stress sufficient to crack,lift, or produce other defects. Accordingly, another desirable propertyof the fill layer is that a combination of the metal layer and the filllayer exhibits less intrinsic stress than would otherwise exist if thefill layer were replaced by an increased thickness of the metal layer.Porous materials constitute one type of material that may provide thelower intrinsic stress, but other materials that might not exhibit aporosity greater than the porosity of the metal layer might also exhibitless stress.

As indicated, a thickness of the fill layer within the line opening maybe greater than a thickness of the metal layer within the line opening.FIGS. 2A-C show forming fill layer 30 to fill all of line opening 36over metal layer 28. Forming the fill layer may include covering themetal layer, at least within the opening, with the fill layer. Such aprocess does not necessarily including filling all of the opening overthe metal layer.

FIGS. 3A-C show the structure of FIGS. 2A-C after chemical-mechanicalpolishing to remove excess fill layer 30. The polishing stops on masklayer 12, which may contain silicon nitride, but may instead stop onmetal layer 28, which may contain titanium nitride. Subsequently, FIGS.4A-C show removing a further excess of fill layer 30 substantiallyselectively with respect to metal layer 28. As is apparently from FIGS.4A-C, some of metal layer 28 is removed while removing further excessfill layer 30, however, the amount removed is small compared to thesignificant thickness of fill layer 30 that is removed. Within thecontext of the present document, substantially selective removal refersto a selectivity ratio of at least about 2 to 1, but preferably at leastabout 5 to 1. Examples of a suitable substantially selective removalprocesses include RIE and a selective wet etch. Known processchemistries exist that are capable of etching polysilicon,TEOS-deposited silicon oxide, or BPSG selectively with respect totitanium nitride. Polysilicon may be selectively etched using HBr orCF₄. TEOS-deposited silicon oxide and BPSG may be selectively etchedusing CF₄ or CH₂F₂.

FIGS. 5A-C show the structure of FIGS. 4A-C after further etching ofmetal layer 28 selectively with respect to fill layer 30. Substantiallyselective removal of metal layer 28 maintains the dimensions of filllayer 30 shown in FIGS. 4A-C. However, it is conceivable that removal ofmetal layer 28 may occur non-selectively such that some additionalportion of fill layer 30 is removed during such process. A suitablesubstantially selective conventional etch using NH₄OH, H₂O₂, anddeionized water removes titanium nitride substantially selectively withrespect to polysilicon and SiO₂. As a result of the uniform deposition,low intrinsic stress, reduced cracking or lifting, and consistentmerging achievable with materials that may be suitable for the largethickness of fill layer 30, but which may not be suitable for metallayer 28 with a large thickness, significant advantage can result fromusing fill layer 30. Namely, stress of the combined metal layer/filllayer may be reduced, yielding more uniform gate electrode structures.Also, average R_(s) as well as variation in R_(s) may be reduced.Further, the occurrence of stringers may be reduced. Another advantageof methods described herein includes protecting the gate dielectric withthe metal layer during processes that may damage the gate dielectric,such as removing excess fill layer. Importantly, forming the FIG. 5A-Cstructures may be implemented using conventional process tools.

An advantage of using conductive material for fill layer 30 includesfacilitating contact of metal layer 28 with other conductive circuitcomponents and it is preferred over insulative material for fill layer30. As is apparent from FIG. 5C, fill layer 30 may provide a landing padarea for contacts. As is apparent from FIG. 5A, the dimensions of aresulting gate electrode containing metal layer 28 determines theportions of pillars 24 and walls 26 that may be used as channel regions.Channel regions may exist where dielectric layer 22 is positionedbetween metal layer 28 and a semiconductive bottom and/or semiconductiveside wall of line opening 36 into substrate 10. Remaining upper portionsof pillars 24 and walls 26 not within such channel may constitutesource/drain regions. Conventional processing, including but not limitedto doping and/or ion implantation, may be used to form the channels andsource/drain regions.

FIG. 9 shows a transistor 120 including source/drain regions 128 formedwithin a substrate 122. A gate dielectric 124 is formed over substrate122 and a gate metal layer 126 is formed over gate dielectric 124. Metallayer 126 is located within a word line trench formed in substrate 122.A gate fill layer 130 fills the entire trench over metal layer 124. Atransistor channel extends between source/drain regions 128 throughsubstrate 122. Transistor 120 with metal layer 126 represents oneexample of a 3-D structure have a channel operationally associated withopposing sides of a gate. One advantage of forming a gate electrode in aword line trench is that it provides a longer gate length for a givenfeature area. A typical planar gate within the same feature area mayhave a much shorter gate length.

According to another aspect of the invention, a transistor gate formingmethod includes forming a gate metal layer containing titanium nitridewithin a gate line opening extending into a semiconductive substrate andfilling all of the opening over the metal layer with a gate fill layercontaining polysilicon. A thickness of the fill layer within the openingis greater than a thickness of the metal layer. The fill layer issubstantially selectively etchable with respect to the metal layer andthe metal layer is substantially selectively etchable with respect tothe fill layer. The fill layer exhibits a porosity greater than aporosity of the metal layer. The metal layer/fill layer combinationexhibits less intrinsic stress than would otherwise exist if the filllayer were replaced by an increased thickness of the metal layer.

According to a further aspect of the invention, a transistor gateforming method includes forming a gate line opening extending into asemiconductive substrate, the opening having a semiconductive bottom andsemiconductive side walls. A gate dielectric is formed within theopening over the semiconductive side walls and semiconductive bottom,the dielectric layer having an insulative bottom and insulative sidewalls. A gate metal layer is formed within the opening over theinsulative bottom and insulative side walls, the metal layer having aconductive bottom and conductive side walls. A gate fill layer is formedwithin the opening over the conductive bottom and conductive side walls.The method includes removing excess fill layer substantially selectivelywith respect to the metal layer while exposing a portion of the metallayer under the fill layer without exposing the gate dielectric underthe metal layer. As mentioned previously, an advantage exists in forminga fill layer followed by removing excess fill layer while exposing themetal layer without exposing the dielectric layer. Namely, removalprocesses directed toward the fill layer may damage the dielectriclayer. Accordingly, substantially selective removal of excess fill layerleaves the metal layer to protect the underlying dielectric layer.Subsequent removal of the metal layer may occur substantiallyselectively with respect to the fill layer. Such a removal process mayexpose the underlying dielectric layer without damaging it.

According to a still further aspect of the invention, a transistor gateforming method includes forming a gate line opening extending into asemiconductive substrate, the opening having a semiconductive bottom andsemiconductive side walls. A gate dielectric layer is formed within theopening over the semiconductive side walls and semiconductive bottom,the dielectric layer having an insulative bottom and insulative sidewalls. A gate metal layer containing titanium nitride is formed withinthe opening over the insulative bottom and insulative side walls, themetal layer having a conductive bottom and conductive side walls. Themethod includes filling all of the opening over the conductive bottomand conductive side walls with a gate fill layer containing polysilicon,a thickness of the fill layer within the opening being greater than athickness of the metal layer. Excess fill layer is removed selectivelywith respect to the metal layer at a selectivity ratio of at least 5 to1 while exposing a portion of the metal layer under the fill layerwithin the opening, but without exposing the dielectric layer under themetal layer within the opening. The exposed portion of the metal layeris removed selectively with respect to the fill layer at a selectivityratio of at least 5 to 1, the fill layer exhibiting a porosity greaterthan a porosity of the metal layer, and the metal layer/fill layercombination exhibiting less intrinsic stress than would otherwise existif the fill layer were replaced by an increased thickness of the metallayer.

Given the variations in methods for forming a transistor gate discussedherein, a variety of transistor structures may result. According to oneaspect of the invention, a transistor structure includes a gate lineopening extending into a semiconductive substrate, the opening having asemiconductive bottom and semiconductive side walls. A gate dielectriclayer is within the opening over the semiconductive side walls andsemiconductive bottom, the dielectric layer having an insulative bottomand insulative side walls. A gate metal layer is within the opening overthe insulative bottom and insulative side walls, the metal layer havinga conductive bottom and conductive side walls. A gate fill layer iswithin the opening over the conductive bottom and conductive side walls.The metal layer/fill layer combination exhibits less intrinsic less thanwould otherwise exist if the fill layer were replaced by an increasedthickness of the metal layer. One or more of the various properties andstructural features of transistor structures discussed herein may beapplied in the present aspect of the invention. By way of example, thefill layer may exhibit the property of being substantially selectivelyetchable with respect to the metal layer.

According to another aspect of the invention, a transistor structureincludes a gate line opening extending into a semiconductive substrate,the opening having a semiconductive bottom and semiconductive sidewalls. A gate dielectric layer is within the opening over thesemiconductive side walls and semiconductive bottom, the dielectriclayer having an insulative bottom and insulative side walls. A gatemetal layer containing titanium nitride is within the opening over theinsulative bottom and insulative side walls, the metal layer having aconductive bottom and conductive side walls. A gate fill layercontaining polysilicon fills all of the opening over the conductivebottom and conductive side walls. A thickness of the fill layer withinthe opening is greater than a thickness of the metal layer, the filllayer exhibits the property of being substantially selectively etchablewith respect to the metal layer. The metal layer exhibits the propertyof being substantially selectively etchable with respect to the filllayer. The fill layer exhibits a porosity greater than a porosity of themetal layer. The metal layer/fill layer combination exhibits lessintrinsic stress than would otherwise exist if the fill layer werereplaced by an increased thickness of the metal layer.

FIG. 10 illustrates generally, by way of example, but not by way oflimitation, an embodiment of a computer system 400 according to anaspect of the present invention. Computer system 400 includes a monitor401 or other communication output device, a keyboard 402 or othercommunication input device, and a motherboard 404. Motherboard 404 cancarry a microprocessor 406 or other data processing unit, and at leastone memory device 408. Memory device 408 can comprise various aspects ofthe invention described above. Memory device 408 can comprise an arrayof memory cells, and such array can be coupled with addressing circuitryfor accessing individual memory cells in the array. Further, the memorycell array can be coupled to a read circuit for reading data from thememory cells. The addressing and read circuitry can be utilized forconveying information between memory device 408 and processor 406. Suchis illustrated in the block diagram of the motherboard 404 shown in FIG.11. In such block diagram, the addressing circuitry is illustrated as410 and the read circuitry is illustrated as 412.

In particular aspects of the invention, memory device 408 can correspondto a memory module. For example, single in-line memory modules (SIMMs)and dual in-line memory modules (DIMMs) may be used in theimplementation that utilizes the teachings of the present invention. Thememory device can be incorporated into any of a variety of designs thatprovide different methods of reading from and writing to memory cells ofthe device. One such method is the page mode operation. Page modeoperations in a DRAM are defined by the method of accessing a row of amemory cell arrays and randomly accessing different columns of thearray. Data stored at the row and column intersection can be read andoutput while that column is accessed.

An alternate type of device is the extended data output (EDO) memorythat allows data stored at a memory array address to be available asoutput after the addressed column has been closed. This memory canincrease some communication speeds by allowing shorter access signalswithout reducing the time in which memory output data is available on amemory bus. Other alternative types of devices include SDRAM, DDR SDRAM,SLDRAM, VRAM and Direct RDRAM, as well as others such as SRAM or Flashmemories.

FIG. 12 illustrates a simplified block diagram of a high-levelorganization of various embodiments of an exemplary electronic system700 of the present invention. System 700 can correspond to, for example,a computer system, a process control system, or any other system thatemploys a processor and associated memory. Electronic system 700 hasfunctional elements, including a processor or arithmetic/logic unit(ALU) 702, a control unit 704, a memory device unit 706 and aninput/output (I/O) device 708. Generally, electronic system 700 willhave a native set of instructions that specify operations to beperformed on data by the processor 702 and other interactions betweenthe processor 702, the memory device unit 706 and the I/O devices 708.The control unit 704 coordinates all operations of the processor 702,the memory device 706 and the I/O devices 708 by continuously cyclingthrough a set of operations that cause instructions to be fetched fromthe memory device 706 and executed. In various embodiments, the memorydevice 706 includes, but is not limited to, random access memory (RAM)devices, read-only memory (ROM) devices, and peripheral devices such asa floppy disk drive and a compact disk CD-ROM drive. One of ordinaryskill in the art will understand, upon reading and comprehending thisdisclosure, that any of the illustrated electrical components arecapable of being fabricated to include DRAM cells in accordance withvarious aspects of the present invention.

FIG. 13 is a simplified block diagram of a high-level organization ofvarious embodiments of an exemplary electronic system 800. The system800 includes a memory device 802 that has an array of memory cells 804,address decoder 806, row access circuitry 808, column access circuitry810, read/write control circuitry 812 for controlling operations, andinput/output circuitry 814. The memory device 802 further includes powercircuitry 816, and sensors 820, such as current sensors for determiningwhether a memory cell is in a low-threshold conducting state or in ahigh-threshold non-conducting state. The illustrated power circuitry 816includes power supply circuitry 880, circuitry 882 for providing areference voltage, circuitry 884 for providing the first word line withpulses, circuitry 886 for providing the second word line with pulses,and circuitry 888 for providing the bit line with pulses. The system 800also includes a processor 822, or memory controller for memoryaccessing.

The memory device 802 receives control signals 824 from the processor822 over wiring or metallization lines. The memory device 802 is used tostore data that is accessed via I/O lines. It will be appreciated bythose skilled in the art that additional circuitry and control signalscan be provided, and that the memory device 802 has been simplified tohelp focus on the invention. At least one of the processor 822 or memorydevice 802 can include a capacitor construction in a memory device ofthe type described previously herein.

The various illustrated systems of this disclosure are intended toprovide a general understanding of various applications for thecircuitry and structures of the present invention, and are not intendedto serve as a complete description of all the elements and features ofan electronic system using memory cells in accordance with aspects ofthe present invention. One of the ordinary skill in the art willunderstand that the various electronic systems can be fabricated insingle-package processing units, or even on a single semiconductor chip,in order to reduce the communication time between the processor and thememory device(s). Applications for memory cells can include electronicsystems for use in memory modules, device drivers, power modules,communication modems, processor modules, and application-specificmodules, and may include multilayer, multichip modules. Such circuitrycan further be a subcomponent of a variety of electronic systems, suchas a clock, a television, a cell phone, a personal computer, anautomobile, an industrial control system, an aircraft, and others.

EXAMPLE

A transistor structure as shown in FIGS. 5A-C was formed bysupercritical fluid deposition of 150 Angstroms of TiN on the structureshown in FIGS. 1A-C. 500 to 2,000 Angstroms of polysilicon with aresistivity of 20 to 200 Ohm-centimeter were formed on the TiN by CVD.Chemical mechanical polishing followed, removing polysilicon andstopping on Si₃N₄ masking layer 12. Polysilicon was recessed into lineopenings 36 using 116 sec. of RIE in a LAM 9400 with 80 to 150 sccm ofHBr and 100 to 200 sccm of He at a pressure of 50 to 100 milliTorr and apower of 125 to 225 Watts. Wet etching at 55° C. using 2 volume % NH₄OHand 3 volume % H₂O₂ in deionized water for 7 min. produced the FIGS.5A-C structure. Scanning electron microscopy of cross-sections andtilted top views did not reveal any cracks or stringers. The processingwas repeated several times within the described parameter ranges,producing highly similar results. Subsequent R_(s) testing revealed arange of 28.9 to 32.3 Ohm/square with a mean of 30.8 Ohm/square. Similarprocessing, except depositing polysilicon alone without the TiN revealeda range of 857 to 1838 Ohm/square with a mean of 1252 Ohm/square.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A transistor gate forming method comprising: forming a gate metallayer within a gate line opening extending into a semiconductivesubstrate; and forming a gate fill layer within the opening over themetal layer, the fill layer being substantially selectively etchablewith respect to the metal layer.
 2. The method of claim 1 wherein theopening is a word line trench.
 3. The method of claim 1 wherein theopening is a RAD opening laterally surrounding a source/drain pillarbetween opposing source/drain walls.
 4. The method of claim 1 whereinthe metal layer is substantially selectively etchable with respect tothe fill layer.
 5. The method of claim 1 wherein the metal layercomprises titanium nitride.
 6. The method of claim 1 wherein the filllayer is semiconductive or conductive.
 7. The method of claim 1 whereinforming the fill layer comprises covering the metal layer, at leastwithin the opening, with the fill layer.
 8. The method of claim 1wherein a thickness of the fill layer within the opening is greater thana thickness of the metal layer.
 9. The method of claim 1 wherein formingthe fill layer comprises filling all of the opening over the metallayer.
 10. The method of claim 1 wherein the fill layer comprisespolysilicon.
 11. The method of claim 1 wherein the fill layer exhibits aporosity greater than a porosity of the metal layer.
 12. The method ofclaim 1 wherein the metal layer/fill layer combination exhibits lessintrinsic stress than would otherwise exist if the fill layer werereplaced by an increased thickness of the metal layer.
 13. The method ofclaim 1 comprising forming the transistor gate in a memory device. 14.The method of claim 13 wherein the memory device is DRAM, SRAM, or flashmemory.
 15. The method of claim 13 wherein the memory device is furthercomprised by a computer system that includes a microprocessor.
 16. Atransistor gate forming method comprising: forming a gate metal layercontaining titanium nitride within a gate line opening extending into asemiconductive substrate; and filling all of the opening over the metallayer with a gate fill layer containing polysilicon, a thickness of thefill layer within the opening being greater than a thickness of themetal layer, the fill layer being substantially selectively etchablewith respect to the metal layer, the metal layer being substantiallyselectively etchable with respect to the fill layer, the fill layerexhibiting a porosity greater than a porosity of the metal layer, andthe metal layer/fill layer combination exhibiting less intrinsic stressthan would otherwise exist if the fill layer were replaced by anincreased thickness of the metal layer.
 17. (canceled)
 18. (canceled)19. A transistor gate forming method comprising: forming a gate lineopening extending into a semiconductive substrate, the opening having asemiconductive bottom and semiconductive side walls; forming a gatedielectric layer within the opening over the semiconductive side wallsand semiconductive bottom, the dielectric layer having an insulativebottom and insulative side walls; forming a gate metal layer within theopening over the insulative bottom and insulative side walls, the metallayer having a conductive bottom and conductive side walls; forming agate fill layer within the opening over the conductive bottom andconductive side walls; and removing excess fill layer substantiallyselectively with respect to the metal layer while exposing a portion ofthe metal layer under the fill layer without exposing the dielectriclayer under the metal layer. 20-35. (canceled)
 36. A transistor gateforming method comprising: forming a gate line opening extending into asemiconductive substrate, the opening having a semiconductive bottom andsemiconductive side walls; forming a gate dielectric layer within theopening over the semiconductive side walls and semiconductive bottom,the dielectric layer having an insulative bottom and insulative sidewalls; forming a gate metal layer containing titanium nitride within theopening over the insulative bottom and insulative side walls, the metallayer having a conductive bottom and conductive side walls; filling allof the opening over the conductive bottom and conductive side walls witha gate fill layer containing polysilicon, a thickness of the fill layerwithin the opening being greater than a thickness of the metal layer;removing excess fill layer selectively with respect to the metal layerat a selectivity ratio of at least 5 to 1 while exposing a portion ofthe metal layer under the fill layer within the opening, but withoutexposing the dielectric layer under the metal layer within the opening;and removing the exposed portion of the metal layer selectively withrespect to the fill layer at a selectivity ratio of at least 5 to 1, thefill layer exhibiting a porosity greater than a porosity of the metallayer, and the metal layer/fill layer combination exhibiting lessintrinsic stress than would otherwise exist if the fill layer werereplaced by an increased thickness of the metal layer.
 37. (canceled)38. (canceled)
 39. A transistor structure comprising: a gate lineopening extending into a semiconductive substrate, the opening having asemiconductive bottom and semiconductive side walls; a gate dielectriclayer within the opening over the semiconductive side walls andsemiconductive bottom, the dielectric layer having an insulative bottomand insulative side walls; a gate metal layer within the opening overthe insulative bottom and insulative side walls, the metal layer havinga conductive bottom and conductive side walls; a gate fill layer withinthe opening over the conductive bottom and conductive side walls, themetal layer/fill layer combination exhibiting less intrinsic stress thanwould otherwise exist if the fill layer were replaced by an increasedthickness of the metal layer.
 40. The structure of claim 39 wherein theopening is a word line trench, the metal layer extending fully up theopening side walls.
 41. The structure of claim 39 wherein the opening isa RAD opening laterally surrounding a source/drain pillar betweenopposing source/drain walls, the metal layer extending only partially upthe opening side walls.
 42. The structure of claim 39 wherein the metallayer comprises titanium nitride.
 43. The structure of claim 39 whereinthe fill layer exhibits the property of being substantially selectivelyetchable with respect to the metal layer.
 44. The structure of claim 39wherein the fill layer is semiconductive or conductive.
 45. Thestructure of claim 39 wherein a thickness of the fill layer within theopening is greater than a thickness of the metal layer.
 46. Thestructure of claim 39 wherein the fill layer fills all of the openingover the metal layer.
 47. The structure of claim 39 wherein the filllayer comprises polysilicon.
 48. The structure of claim 39 wherein thefill layer exhibits a porosity greater than a porosity of the metallayer.
 49. The structure of claim 39 wherein the transistor structure isin a memory device.
 50. The structure of claim 49 wherein the memorydevice is DRAM, SRAM, or flash memory.
 51. The structure of claim 49wherein the memory device is further comprised by a computer system thatincludes a microprocessor.
 52. A transistor structure comprising: a gateline opening extending into a semiconductive substrate, the openinghaving a semiconductive bottom and semiconductive side walls; a gatedielectric layer within the opening over the semiconductive side wallsand semiconductive bottom, the dielectric layer having an insulativebottom and insulative side walls; a gate metal layer containing titaniumnitride within the opening over the insulative bottom and insulativeside walls, the metal layer having a conductive bottom and conductiveside walls; a gate fill layer containing polysilicon filling all of theopening over the conductive bottom and conductive side walls, athickness of the fill layer within the opening being greater than athickness of the metal layer, the fill layer exhibiting the property ofbeing substantially selectively etchable with respect to the metallayer, the metal layer exhibiting the property of being substantiallyselectively etchable with respect to the fill layer, the fill layerexhibiting a porosity greater than a porosity of the metal layer, themetal layer/fill layer combination exhibiting less intrinsic stress thanwould otherwise exist if the fill layer were replaced by an increasedthickness of the metal layer.
 53. (canceled)
 54. (canceled)